Lake Ossiach is located in the southern Nock Mountains range of the Gurktal Alps along the road from Villach to Feldkirchen.

The main inflow is Tiebel Creek in the eastern bay, where the Bleistatt Moor has been re-naturalised.

The lake empties via Seebach Creek into the Drava (German: Drau) River.

Mount Gerlitzen rises over the northern side of the lake, reaching 1,909 m (6,263 ft) at its summit.

From Annenheim, the Kanzelhöhe subpeak of Mount Gerlitzen can be reached by a cable car built in 1928 by the Bleichert engineering company.